<!DOCTYPE html>
<html lang="zh-CN">
  <head>
    <meta charset="UTF-8" />
    <meta http-equiv="X-UA-Compatible" content="IE=edge" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title></title>
  </head>
  <body>
    <canvas id="myCanvas"></canvas>
    <script>
      var c = document.getElementById("myCanvas");
      var ctx = c.getContext("2d");
      ctx.beginPath();
      ctx.lineWidth = "6";
      ctx.strokeStyle = "red";
      ctx.arc(100, 75, 50, 0, 2 * Math.PI);
      ctx.stroke();
    </script>
  </body>
</html>
